A novel scheme of plastic optical fiber (POF) based arc flash sensor capable of tracing arc event locations is presented. Incident position of flash light can simply be known by measuring the ratio of intensities at both fiber-ends, since the intensity of the flash light assisted by side-coupling of the fiber is generally attenuated a the fiber length. The arc flash sensor which can cover a wide range up to 10 m with a high spatial resolution of &plusmn;10 cm is experimentally demonstrated using the POF. Arc flash intensity can also be known by analyzing the coupled light intensity level at both fiber ends.

We present an arc flash sensor that can trace the arc event position as well as intensity by utilizing conventional plastic optical fibers (POFs). In order to check the possibility as a light-receiving sensor, we experimentally confirm that the externally irradiated flash light can be coupled into the fiber core through the surface of POF without any additional treatment. After the incident light is divided in two optical paths toward opposite directions, they have the different attenuation values determined by the propagation distance. Since the optical transmission loss of a POF is constant regardless of the irradiated energy, the intensity ratio for two signals measured at both fiber ends is given as a function of position. The experimental results show that we can successfully trace the event position from this intensity ratio. In addition, it is possible to define the illuminated energy by comparing the absolute value of the intensity measured from one side. According to the experimental results, the proposed sensor has a relatively fine spatial resolution, ±10 cm, despite having a simple structure.

This paper suggests an optical printed circuit board (OPCB) having new optical coupling structures, including a laser-drilled and under-filled structure (LD-UFS) and a vertical waveguide structure (VWS). The suggested OPCB has the features of high-speed data transmission as well as highly efficient optical coupling because it was fabricated with low-dielectric and transparent electrical PCB materials through a PCB compatible process. To evaluate and compare the optical and electrical performances of the suggested OPCB with those of other OPCBs, the various types of OPCBs were fabricated and measured. The optical coupling losses of the LD-UFS and the VWS were measured with excellent results of 9.8 and 7.8 dB, respectively, which are lower than that of the basic structure. The electrical 3-dB bandwidth of the OPCB was also evaluated up to more than 40 GHz.

We have demonstrated a refractive index sensor based on a fiber optic Fabry–Perot (FP) interferometer with an open air cavity fabricated using a one-step mechanical sawing technique. The sensor head consists of a short FP cavity near the fiber patch cord tip, which was assembled by joining a ceramic ferrule and a single-mode fiber together. Owing to the open air cavity in the sensor head, various liquid samples with different refractive index can fill in-line air cavity, which makes the device usable as a refractometer. Moreover, due to the sensor head encircled with the robust ceramic ferrule, the device is attractive for sensing measurement in harsh environments. The sensor was tested in different refractive index solutions. The experimental result shows that the attenuation peak wavelength of the sensor is shifted toward a shorter wavelength with increasing refractive index, and the refractive index sensitivity is ∼92.5 nm/refractive index unit (RIU) and 73.75 dB/RIU . The proposed sensor can be used as an in-line refractometer for many potential applications in the sensing field.

We demonstrate an optical planar waveguide sensor that can be used to measure the direction and intensity of
physical force. The interferometric structure, on which the proposed sensor is based, introduces an interference
pattern in wavelength. Its phase is shifted by the external force. On the other hand, since the cross-sectional effective
refractive index profile is asymmetric because of the core formed on one side of silica substrate, the phase shift
appears with respect to the direction of the external force against the surface. Therefore, we can measure the
direction and intensity of the applied force by monitoring the phase change.

We propose the temperature-insensitive bending sensor based on a hole-assisted single polarization fiber (SPF). Without
fiber grating structures, the SPF-based sensing probe can provide the sensing technique to measure the bending change.
If bending is applied to the SPF, two cutoff wavelengths are shifted to shorter wavelengths and the transmission power is
diminished because the structural deformation of the SPF induced by bending changes birefringence depending on
principle axes of the SPF. However, the applied temperature variation has no effect on the birefringence change severely
and two cutoff wavelengths are not shifted by changing temperature. Therefore, the proposed SPF-based sensing probe
with temperature insensitivity can measure the bending change effectively.

We describe an ultra-thin and low-power optical interconnect module for mobile electronic devices such as mobile phones and notebooks. The module was fabricated by directly packaging optic and electronic components onto a thin and flexible optical printed circuit board having a size of 70×8×0.25 mm. The completed active module has features of thinness (0.5 mm), small size (7×5 mm), very low total power consumption (15.88 mW), and high data rate transmissions (2.5 Gbps).

We integrate transmitting and receiving parallel optical subassemblies (POSAs) that are suitable for high-speed and parallel optical modules between optical components by using a simple and high-accuracy alignment technique. Characteristics of the proposed POSAs include a low coupling loss of 0.75 dB, a wide bandwidth for 10 Gbits/s transmission per channel, and low optical and electrical crosstalk of less than 30 dB. As a result, a data transmission rate of 10 Gbits/s×12 channels is well demonstrated with clean eye diagrams.

We present a new configuration for a polymer wavelength division multiplexing (WDM) filter based on multimode interference. We developed a hybrid integrated subassembly module for 1.31- and 1.55-µm bidirectional operation. Active devices including a laser diode with a monitoring photodiode and a receiving photodiode were integrated on a silicon optical bench (SiOB) platform using a flip-chip bonding technique. A polymer WDM filter chip made of polymethylmethacrylate was fabricated using a hot embossing technique. We then investigated the optical performance of the transmitter and receiver subassembly module using a SiOB platform. This hybrid integrated subassembly module exhibited bidirectional 2.5-Gbit/s signal modulation with a minimum sensitivity of −20.5 dBm at a bit error rate of 10−10 and an optical crosstalk of −35 dB.

We propose a simple method to self-compensate temperature which can affect the sensitivity of palladium-based
hydrogen gas sensor. When a long-period fiber grating is fabricated in a double cladding fiber, the fundamental core
mode is coupled to the inner cladding mode as well as the outer cladding mode. Since the inner cladding mode is
insensitive to the external contact, it is independent to the thin palladium layer coated out of cladding surface. Thus, the
spectrum corresponding to outer cladding modes reflects the reaction between hydrogen and palladium while that of the
inner cladding mode indicates the ambient temperature only.

We demonstrate a simple but highly sensitive hydrogen sensor based on palladium-coated long-period fiber grating
(LPG) inscribed in low core index fiber, which induces higher order cladding modes. As palladium layer absorbed 4% of
hydrogen gas, the dual resonant wavelengths of the higher order cladding mode (LP<sub>08</sub>) are shifted to the opposite
direction. The spectral sensitivity was much higher than those of other fiber-optic palladium-coated hydrogen sensors.

A rigid flexible optical electrical printed circuit board (RFOE-PCB) with both electrical layers and an optical layer was fabricated using a conventional PCB manufacture process. The RFOE-PCB is applicable to fold-type mobile devices such as mobile phones and laptop computers. The RFOE-PCB was designed to be embedded with a flexible 45-deg-ended optical waveguide, which was made using a polymeric material. The precise lamination between an electrical layer and an optical layer was achieved by a passive alignment method. We carried out the repetitive folding test and an environment test for physical and optical reliability suitable for mobile devices. Data transmission of 2.5 Gb/s was demonstrated with a clear eye diagram using the fabricated RFOE-PCB.

A practical optical link system was prepared with a transmitter (Tx) and receiver (Rx). The optical TRx module
consisted of a metal optical bench, a module printed circuit board (PCB), a driver/receiver IC, a VCSEL/PD array, and
an optical link block composed of plastic optical fiber (POF). For the optical interconnection between the light-sources
and detectors, an optical wiring method has been proposed to enable easy assembly.
This paper provides a method for optical interconnection between an optical Tx and an optical Rx, comprising the
following steps: (a) forming a light source device, an optical detection device, and an optical transmission unit on a
substrate (metal optical bench (MOB)); (b) preparing a flexible optical transmission-connection medium (optical wiring
link) to optically connect the light source device formed on the substrate with the optical detection device; and (c)
directly connecting one end of the surface-finished optical transmission connection medium with the light source device
and the other end with the optical detection device. A chip-to-chip optical link system constructed with TRx modules
was fabricated and the optical characteristics were measured. The results clearly demonstrate that the use of an optical
wiring method can provide robust and cost-effective assembly for vertical-cavity surface-emitting lasers (VCSELs) and
photodiodes (PDs). We successfully achieved a 5 Gb/s data transmission rate with this optical link.

Passive optical components for optical interconnection using hybrid optical printed-circuit boards (PCBs) where electrical and optical layers are integrated into one board has been studied. We present detailed fabrication processes and optical characteristics of optical PCBs and connectors for optical coupling between vertical and horizontal directions. Two kinds of optical PCBs, polymer-waveguide-embedded and silica-fiber-embedded PCBs, were prepared. For the polymer-waveguide-embedded PCB, the polymer waveguide was formed lithographically on a FR-4 board and its core has 100 &mu;m width and 60 &mu;m thickness. The waveguide-defined board was covered with another FR4 plate and then laminated at 185&deg;C under the pressure of 35 kg/cm<sup>2</sup>. After lamination the transmission loss of the waveguide was -0.53 dB/cm. For the fiber-embedded PCB, fibers with 100 &mu;m core diameter were inserted in grooves formed on a FR-4 board and they followed a similar lamination processes. The propagation loss of the fiber-embedded board at 850 nm was negligible in board scale. We also prepared 2 types of connectors for optical coupling between the surface mounted transmitter or receiver modules and the optical PCBs; 45&deg;-ended fiber block and 90&deg;-bent fiber connector. The insertion losses of the 2 kinds of connectors were, respectively, -0.15 dB and -0.25 dB. The best combination between the optical PCBs and connectors in view of optical characteristics and packaging is fiber-embedded board and 90&deg;-bent fiber connector. They show successfully optical link of 2.5 Gbps with a very low coupling losses of -4.4 dB and a low optical crosstalk of -53 dB.

A simple method for fabricating fiber-embedded boards using a grooving technique is described that is quite cost effective and fully compatible with conventional printed circuit board (PCB) processes with no necessity for a specially designed wiring machine. FR-4 plates are grooved using a dicing saw machine and followed by placing optical fibers into the grooves. The fiber-embedded PCBs are laminated by conventional PCB processes at a temperature of 180°C for 1 h under 47 kg/cm2 of pressure. The 50/125-µm glass fibers, and the polyimide-coated glass fibers are laminated successfully. In the fiber-embedded boards with a length of 10 cm, the variation of center positions of the embedded glass fibers is about ±5 µm. The transmitted optical power through the fiber-embedded boards shows a good uniformity of less than ±0.5 dB variation from the average value for the 12 fiber channels. Data transmission through the board at data rates of 2.5 Gbits/s is achieved. After confirming the successful laminations and the data transmission with the small-scale fiber-embedded boards, a large-scale prototype of the fiber-embedded board for a backplane application is successfully fabricated.

We demonstrated a new architecture of the optical interconnection system which can be applied in the waveguide-embedded optical printed circuit board (PCB). We used 45&deg; ended optical connection rods as a medium to guide light paths perpendicularly between surface-emitting lasers (or photodiode) and waveguides. A polymer film of multimode waveguides with cores of 100&#956;m x 65&#956;m was sandwiched between conventional PCBs. We made through-holes with a diameter of ~140&#956;m on the PCB, passing through the waveguide cores, using Ti-sapphire laser drill. The optical rods were made of the segment of multimode silica fiber ribbon. One end of the fiber segment was cut with 45&deg; and the other end with 90&deg; by using the high power laser cutting technique. These fiber rods were inserted into the through-holes formed in the PCB, adjusting the insertion depth to locate the 45&deg;-end of rods near the waveguide core. From this interconnection system, we achieved 12channels optical transmission link through a waveguide with a channel pitch of 250&#956;m in the optical PCB. This new interconnection structure using the optical connection rods is well compatible with the fabrication processes of conventional electronic PCB which is employing the through-hole formation by laser drill and the lamination of plastic films by compression.

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